1. Field of the Invention
The present invention relates to a multi-electron beam device and to an image display device using the same, having a large number of electron emitting elements arranged in a plurality of rows.
2. Related Background Art
A cold cathode element for example disclosed by M. I. Elinson and others has been known as the element by which electron emission may be achieved based on a simple structure. [Radio Engineering Electron Physics (Radio Eng. Electron Phys.) Vol.10, pp.1290-1296, 1965].
It uses the phenomenon that electron emission occurs when an electric current is caused to flow through a film having a small area formed on a substrate in parallel to the film surface thereof, which is generally called as a surface conduction type electron emitting element.
Among those made known to the public as such surface conduction type electron emitting elements are: one using SnO.sub.2 (Sb) thin film developed by Elinson and others as described above; one based on Au film [G. Dittmer "Thin Solid Films" (G. Dittmer: "Thin Solid Film), Vol.9, p.317, (1972)]; one based on an ITO film [M. Hartwell and C. G. Fonstad: "IEEE Trans" ED Conf. (M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.") p.519, (1975)]; one based on Carbon film [Araki Hisashi and Others: "Shinku", Vol.26, No.1, p.22, (1983)]. Also, there is known one using Pd, in place of the above SnO.sub.2, Au or ITO, as a material of an electron emitting portion, which is described in Japanese Patent Application Laid-open No. 1-279542.
Further, in addition to the surface conduction type electron emitting elements, such cold cathode elements as an MIM type electron emitting element and a finely fabricated field emission electron gun have been reported.
These cold cathode elements have such advantages as that:
1) a high electron emission efficiency may be achieved;
2) they are easily fabricated because of their simple structure; and
3) a large number of elements may be arranged into an array on a single substrate.
Thus the present inventors have already proposed a method as shown in FIG. 1 as the method in which a large number of such cold cathode elements are densely arranged into an array and at the same time resistance of the electric wiring thereof is reduced. In the figure, ES represents an electron emitting element and E.sub.1 -E.sub.m+1 denote distributing electrodes, forming an array having "m" rows of electron emitting elements. This functional region is called an electron emitting element part.
In this device, any one of the rows may be selectively driven, i.e., by for example applying a driving voltage V.sub.E [V] only to an electrode E.sub.1 and 0[V] to electrodes E.sub.2 -E.sub.m+1, a driving voltage of V.sub.E [V] is applied only to the elements in the first row where only the elements in that row are caused to emit electron beam. In general, it suffices to apply V.sub.E [V] to electrodes E.sub.1 -E.sub.n and to apply 0[V] to electrodes E.sub.n+1 -E.sub.m+1 in order to drive the "n"th row, and, in the case where none of the columns is to be driven, it suffices to bring all of E.sub.1 -E.sub.m+1 to the same potential (for example 0[V]).
Such a multi-electron beam source capable of row-sequential drive is expected to be applicable for example to a flat panel CRT, since an electron beam source of XY-matrix type may be easily formed by providing grid electrodes perpendicularly to the rows of the elements.
In the case where the multi-electron beam source as shown in FIG. 1 is driven by an electric circuit, however, there has been a problem that a spike-like voltage is applied to those rows of elements which, in theory, are to halt. FIG. 2 and FIG. 3 are provided to explain such a problem.
First, FIG. 2 shows a typical example of the circuit for use in driving the multi-electron beam source of FIG. 1 as described above. In the figure, switching elements such as field-effect transistors (FET) are connected in the manner of a totem pole to the distributing electrodes represented by E.sub.1 -E.sub.m+1, where, by suitably controlling gate signals GP.sub.1 -GP.sub.m+1 and GN.sub.1 -GN.sub.m+1 of the respective FET, 0[V] (ground level) or VE[V] may be selectively applied to each distributing electrode. This functional region is called a driving circuit part.
FIG. 3 is a graph exemplifying the voltage to be applied to each section when driving the multi-electron beam source of FIG. 2 as described. As shown in (1) of the figure, the case is assumed where the rows of the elements are sequentially driven with in-between halt periods, starting from the first row. (Such driver means is practiced when a multi-electron beam source is utilized for a flat panel CRT.)
In performing such drive, rectangular voltage pulses of V.sub.E [V] are applied to the distributing electrodes E.sub.1 -E.sub.4 at timings as indicated by (2)-(5) of the same figure. For example, since the difference in voltage between (2) and (3) is applied to the first row, V.sub.E [V] is applied thereto at the first row's driving timing as indicated in (1). Thereafter, the difference voltage between (3) and (4) to the second row and the difference voltage between (4) and (5) to the third row are respectively applied in a similar manner.
However, when the voltage applied to each row of the elements is actually observed for example using an oscilloscope, it is seen that, as indicated in (6)-(8) of the same figure, a spike-like voltage SP(+) (indicated by dotted line in the figure) or SP(-) (indicated by solid line in the figure) is applied at timings at which another row of the elements is to be turned on or to be turned off.
Since such spike-like voltage is applied to the electron emitting elements, there has been a problem as follows. That is, since the electron beam is inevitably emitted due to the spike-like voltage at timings where it should be halted, an emission of light occurs at such timings where no light is to be emitted for example when they are adapted to the electron beam source of a flat panel CRT. The problem thus occurs that the contrast in an image is reduced.
In particular, when the negative voltage SP(-) of these spike-like voltages is applied to the electron emitting element, the electron emitting characteristics of each element may deteriorate at a considerably faster rate or be instantaneously destroyed, causing a large problem in applying the multi-electron beam source to such as a display device.
Such spike-like voltage occurs presumably because a shift in timing results in the waveform of the voltage applied to each electrode as indicated by the above described (2)-(5). For example, in the case of the first row, the electrode E1 and the electrode E2 should be simultaneously switched as 0[V].fwdarw.V.sub.E [V] (or V.sub.E [V].fwdarw.0[V]) at the timing where a row of the second or after is to be turned on (or off). If a shift occurs in such timing, application of spike-like voltages as indicated in (6) results.
At this time, whether spike SP(+) of a positive voltage results or spike SP(-) of a negative voltage results depends on which one of the applied voltage for E.sub.1 and the applied voltage for E.sub.2 is switched in advance.
The reason for the occurrence of a shift in timing of voltage waveform to be applied to each electrode includes: shift in gate signals GP.sub.1 -GP.sub.m+1 and GN.sub.1 -GN.sub.m+1 of FET's of the driver circuit as shown in FIG. 7 described above; and the fact that switching time varies according to the variance in characteristic of each FET.
Complete elimination, in terms of the electric circuitry, of the spike-like applied voltage SP(-) by adjusting the shift in the gate signals and/or the variance in FET characteristics is technologically very difficult and, from the viewpoint of costs, cannot be regarded as a practical solution.